Suppress output from background fetch

However, show it when there was an error. This is important for the case that a
fork that you have as a remote was deleted, in which case the command log is the
only way to get notified about that.

pkg/commands/git_commands/sync.go

@@ -79,6 +79,7 @@ func (self *SyncCommands) FetchBackgroundCmdObj() *oscommands.CmdObj {
 
 	cmdObj := self.cmd.New(cmdArgs)
 	cmdObj.DontLog().FailOnCredentialRequest()
+	cmdObj.SuppressOutputUnlessError()
 	return cmdObj
 }